In the conventional art, a construction structure is built by pouring concrete after installing a mold and reinforcements on the spot. However, the conventional method has a problem that the quality of the construction structure is greatly influenced by surrounding circumstances.
Accordingly, a pre-cast method is being actively supposed, by which members of a structure are provided in advance, and the members are an installed in the working place. The method has an advantage that the quality of the structure can be ensured regardless of the surrounding circumstances.
The method may have a problem that constructing equipment has to be additionally prepared near the working place, since each member of the structure has to be provided in advance. However, under the construction in a large scale, the construction duration and costs may be reduced by the method. Accordingly, the problem does not serve as a severe one.
In case of building a bridge, research is being actively performed, by which only piers are built according to an installation technique on the working place, and copings or girders manufactured in advance are installed.
For instance, according to a FSLM (Full Span Launching Method), all of girders for a bridge are provided in advance on a manufacturing line near the actual working place, and then sequentially undergo a temporary work at an upper side of piers, which is also referred to as a PSM (Pre-cast span method).
FIGS. 1 and 2 are schematic diagrams showing a basic concept of a construction method for a girder in a bridge according to the conventional art.
As shown in FIG. 1, a bridge is constructed by installing girders 30 on each upper surface of copings 20 installed above piers 10. As shown in FIG. 2, the girders 30 are sequentially moved to each section formed between the piers 10 and the copings 20 in a forward direction.
More concretely, the girder 30 is carried to a temporary work position by a vehicle 40 for carrying a girder, the vehicle moving on an upper surface of the installed girder 30. Then, the girder is pulled up by a crane thus to be installed at the temporary work position.
However, the conventional method has a disadvantage to be applied only to specific circumstances such as a railroad bridge, not to a general roadway bridge.
The railroad bridge has a characteristic that a secondary dead load (a load of a structure to be build on an upper surface of another bridge on a cobble road) or a live load (a load of a train) is much larger than a first dead load (a load of a bridge itself). With consideration of the specific characteristic, the railroad bridge is designed so that the piers 10 can have strength enough to resist large load exceeding the first dead load.
In order to minimize influence on structural stability, the girder 30 to be subsequently installed is carried through the installed piers 10, copings 20, and girder 30.
On the contrary, the general roadway bridge has a characteristic that the secondary dead load or the live load is smaller than the first dead load. Accordingly, the general roadway bridge is constructed so that each member can have strength enough to resist only the first dead load. As a result, a technique for building a railroad bridge need not to be applied to the general roadway bridge.
In order to apply a pre-cast method not by the building technique in the working place, to the roadway bridge, an additional means needs to be provided.